Method for producing a metal layer on a surface

ABSTRACT

The invention concerns a method for producing a metal coating on a portion of the surface of a substrate of a microelectronic device, wherein it comprises, using a modified nucleic acid strand comprising a nucleic acid strand structure, at least one metal nanoparticle and/or a metal atom and at least one chemical function, at least one step of fixing the chemical function of the at least one modified nucleic acid strand on the portion of the surface of the substrate.

FIELD OF THE INVENTION

The present invention relates to a microelectronic device. It concerns in particular the production of a metal-based coating on a surface, in particular three-dimensional, of a substrate.

TECHNOLOGICAL BACKGROUND

Three-dimensional (3D) integration is becoming a method of exploration that is very much followed in microelectronics. It makes it possible in particular to assemble chips together on a vertical axis thus assisting the production of ever more compact and high-performance components; the length of the interconnections being reduced compared with a conventional assembly. It is consequently necessary, for this three-dimensional technology, to master the step of deposition of 3D materials such as the insulators or metals.

Furthermore, through electrical connections, more commonly referred to by the English acronyms “TSV”, standing for “through-silicon vias”, when the substrate is made from silicon, “TGV”, standing for “through-glass vias”, when the substrate is made form glass, or “TPV”, standing for “through-polymer vias”, when the substrate is made from polymer, are used in microelectronic components in order to connect one face of a component to its opposite face.

Because of the increase in density of electrical connections, it is becoming essential to reduce their dimension in the plane, and in particular their diameter (of around a few microns), while keeping a depth of around a hundred microns. The steps of deposition of insulators and conductive materials are therefore becoming key technical points.

The etching of a substrate when it is made from silicon is generally carried out by deep reactive ion etching (DRIE). The insulation of the walls of a via is obtained by deposition of an insulator (for example silicon dioxide SiO₂), generally by the chemical vapour deposition (CVD) method. Depending on the maximum temperature acceptable for the substrate, several methods exist in a temperature range lying between 150° C. and 400° C. If the substrate so permits, a thermal oxidation can be envisaged (temperature above 800° C. for example). The deposition of the metal conductor takes place in three steps: the first consists of depositing an attachment layer on the insulator (for example titanium on SiO₂), the second of depositing a diffusion-barrier layer (nickel or titanium nitride for example), the third of depositing a layer of metal (copper or gold for example) that will serve as a seed layer or for the growth of a deposition by electrodeposition (copper for example).

The entire problem, when the shape factor (the depth of the via with respect to the diameter of the via, also referred to as aspect ratio—AR) increases, is finding solutions for obtaining a conforming deposition, that is to say one covering the walls of the via uniformly.

Furthermore, the layers formed by these traditional deposition techniques are not conforming, and therefore do not have a uniform thickness at every point on the surface of the substrate. The sides of the trenches and vias may in particular be covered with an insufficient thickness of the layer, then causing imperfect subsequent filling having defects in the material (referred to as voids). In addition, the layers produced on the sides of the patterns have by nature an appearance different from that deposited on the flat surface of the substrate (top and bottom of the trenches and vias). This may lead to impaired reliability performances, such as resistance to electromigration. In other words, the defect in conformity is revealed not only by differences in thickness; defects of continuity and adhesion of the layer on the sides of the trenches and vias may also result therefrom.

These drawbacks make it very tricky to use PVD technology in the advanced generations of integrated circuits where the transverse dimensions of the trenches and vias are very small (around a few tens of nanometres) and where the aspect ratios may be high. With regard to physical vapour deposition, the method reaches its limits with an aspect ratio of around 10 to 1 (denoted 10:1). Metallic deposition by CVD also finds limits in the aspect ratio, but especially in the technological cost. Likewise, atomic layer deposition is an expensive alternative (slow process) compared with chemical vapour deposition. The solution therefore at the present time seems to lie in wet methods, which are the best suited for meeting the specification: aspect ratio and cost.

In this context, solutions through the deposition of a layer in a liquid medium have an advantage by involving a method by electrografting of an organic precursor on a conductive or semiconductive substrate. It is then possible to produce a stack of layers by successive deposition of an isolation layer, then a diffusion-barrier layer followed by a seed layer. Electrografting consists of a method of wet deposition based on the initiation and then electro-induced polymerisation of electroactive monomers. The document FR-A-2933425 describes a method for producing an electrically insulating film by electrografting as well as the deposition of a copper diffusion barrier. These methods make it possible to obtain conforming films, with a thickness of between a few nanometres and 500 nanometres for aspect ratios that may be as much as 20:1. The method described in the document FR-A-2933425 consists of depositing an organic film by electrografting on a conductive or semiconductive surface. The electrografting is obtained by immersing the conductive or semiconductive surface in a solution containing the organic precursor or precursors and applying an electrical potential to said surface.

One object of the present invention is to propose an alternative deposition method that will be able to be used, for example, for producing a through via the aspect ratio of which may be as much as, for example, 50:1.

Moreover, it may be particularly advantageous to propose a solution for being able to lay down at least one monolayer of nanoparticles with geometric shapes, for example, in three dimensions.

It would also be advantageous to propose a method for forming a uniform and homogeneous coating on a surface, and for example three-dimensional, while making it possible to obtain a high aspect ratio such as 50:1.

The present invention sets out to afford a solution for achieving at least one of these objectives.

SUMMARY OF THE INVENTION

The invention concerns, according to one aspect of embodiments, a method for producing a metal-based coating on at least a portion of the surface of a substrate of a microelectronic device, characterised in that it comprises, using a modified nucleic acid strand comprising a nucleic acid strand structure, at least one metal-based nanoparticle and/or a metal atom and/or a chemical function, and at least one step of fixing the modified nucleic acid strand to the portion of the surface of the substrate by means of at least one chemical function.

According to the invention, the concept of “microdevice” includes that of “nanodevice”. Moreover, nucleic acid strand means both a single strand and a double strand.

Because it is possible to synthesise nucleic acid that will comprise, within a double strand, a metal atom or a chain of metal atoms that may be of different chemical natures, or at the end of a single strand a metal-based nanoparticle, it therefore appears possible to produce metal-based depositions using this metallised nucleic acid within it and/or on the periphery.

The method thus involves precursors obtained from modified nucleic acid strands. It is therefore a wet method that will make it possible to coat the walls for example of a cavity (in particular of a via) and/or of a relief (in particular of a pad), for example, by precursors of nanometric size present on the modified nucleic acid strands. In a particularly advantageous manner, these will make it possible, for example, to produce insulating layers, a diffusion barrier and the metal seed layer for a chemical (electroless) deposition, which will then be able to be followed by a conventional electrochemical deposition (ECD). The method involves nucleic acid strands comprising both nanoparticles and/or atoms as well as at least one chemical function that will make it possible to graft the strand onto the three-dimensional surface. Advantageously, the invention will apply not only to three-dimensional surfaces but also for example to two-dimensional surfaces.

Advantageously, the method makes it possible to coat at least one monolayer of nanoparticles of geometric shapes, for example, in three dimensions.

Advantageously, the invention makes it possible to obtain a high aspect ratio.

Furthermore, the invention does not necessarily require the external action of an electrical field. Nevertheless, according to a particular embodiment, it is possible advantageously to use an external magnetic field when the nanoparticle or the metal atom is magnetic, such as for example iron (Fe), cobalt (Co) or nickel (Ni).

The invention also concerns, according to other aspects, the use of at least one modified nucleic acid strand comprising a nucleic acid strand (or skeleton), at least one metal-based nanoparticle and/or a metal atom, configured to form a metal-based coating on at least a portion of the surface of a substrate.

BRIEF INTRODUCTION OF THE FIGURES

Other features, aims and advantages of the present invention will emerge more clearly from the detailed description of embodiments thereof which are illustrated by the following accompanying drawings, in which:

FIG. 1 illustrates a schematic view of a modified nucleic acid double strand of the DNA type on which, at the periphery of the double strand, and in particular on the structure of the strand, an atom or nanoparticle has previously been grafted.

FIG. 2 illustrates a schematic view of a modified nucleic acid double strand on which, on a structure of the strand, between two bases, an atom or a nanoparticle has previously been grafted.

FIGS. 3A and 3B are schematic representations of a modified single nucleic acid strand on which, at a first end of the strand, a nanoparticle and, at the other end, a chemical function have previously been grafted.

FIG. 4 illustrates the step of forming an interconnection pattern on the substrate.

FIG. 5 illustrates the step of treating the three-dimensional surface of the substrate.

FIG. 6 illustrates a step of grafting at least one modified nucleic acid strand, comprising the structure of the strand, at least one atom or a nanoparticle and a chemical function.

FIG. 7 illustrates a heating step configured to partially or totally destroy the structure of the modified nucleic acid strand.

FIG. 8 illustrates the step of making an electrochemical deposition on the coating.

FIGS. 9A and 9B illustrate an example of a three-dimensional surface on which the coating according to the present invention can be produced while ensuring uniformity of the layer and distribution over the entire surface.

FIG. 10A illustrates an example of a three-dimensional surface of a substrate on which a cavity has previously been produced. The sides of the cavity are covered with a hydrophilic or hydrophobic film enabling the modified nucleic acid strands to be fixed.

FIG. 10B illustrates an example of a three-dimensional surface of a substrate on which a cavity has previously been produced. Following irradiation by ultraviolet rays, only the sides of the cavity protected from the rays are covered with modified nucleic acid strands.

The drawings are given by way of examples and are not limitative of the invention. They constitute schematic outline representations intended to facilitate understanding of the invention and are not necessarily to the scale of practical applications. In particular, the relative thicknesses of the various layers and films are not representative of reality.

DETAILED DESCRIPTION

In the context of the present invention, the term “on” does not necessarily mean “in contact with”. Thus, for example, the deposition of a layer on another layer does not necessarily mean that the two layers are directly in contact with each other but means that one of the layers at least partially covers the other while either being directly in contact therewith or being separated therefrom by a film, yet another layer or another element.

Before beginning a detailed review of embodiments of the invention, optional features, which may optionally be used in combination or alternatively, are stated below:

-   -   The step of fixing a modified nucleic acid strand is performed         by means of the chemical function.     -   At the end of the step of fixing the chemical function, a step         of at least partial destruction of the nucleic acid strand         structure (or skeleton) and the chemical function.     -   The step of at least partial destruction of the nucleic acid         strand structure and/or of the chemical function comprises a         heating step configured so as to partially or totally destroy         the nucleic acid strand structure and/or the chemical function.     -   The at least one surface portion of the substrate is a         three-dimensional surface.     -   Said surface portion is chosen from a cavity and/or a relief.     -   Said surface portion is a cavity and the cavity has a depth         greater than its width.     -   The step of fixing the at least one modified nucleic acid strand         on the portion of the surface of the substrate is obtained by         putting the surface of the substrate in contact with a bath         comprising at least one modified nucleic acid strand.     -   The portion of the surface of the substrate comprises a chemical         group configured so as to interact with the chemical function         fixed on the structure of the at least one modified nucleic acid         strand.     -   Several steps of fixing modified nucleic acid strands are         performed.     -   The modified nucleic acid strands are identical or different         through the structure of their respective strands and/or through         their respective chemical functions and/or through the nature         and/or dimensions of the metal-based nanoparticles and/or metal         atoms. Advantageously, the modified nucleic acid strands have         variable natures.     -   After the steps of fixing the modified nucleic acid strands, a         single step of destruction of the nucleic acid strand structures         is performed.     -   Prior to said at least one step of fixing the chemical function         of the at least one modified nucleic acid strand on the portion         of the surface of the substrate, a step of deposition of a         grafting layer on at least the portion of the surface of the         substrate.     -   The grafting layer is deposited over the entire surface of the         substrate.     -   The portion of the surface of the substrate or the grafting         layer comprises a first chemical group or a hydrophilic or         hydrophobic material.     -   The chemical function comprises a second hydrophilic or         hydrophobic chemical group.     -   The metal-based coating forms part of a via.     -   The metal atom is chosen from copper, nickel, aluminium,         palladium, gold or silver.     -   The metal nanoparticle is chosen from a metal, a metal oxide, a         metal nitride or a metal carbide.     -   Prior to the step of fixing the chemical function of at least         one modified nucleic acid strand on the portion of the surface         of the substrate, a step of irradiation by ultraviolet rays of         the portion of the surface of the substrate intended to receive         the metal-based coating.     -   Prior to the step of fixing the chemical function of at least         one modified nucleic acid strand on the portion of the surface         of the substrate, a step of irradiation by ultraviolet rays of         the entire surface of the substrate, except for the portion         intended to receive the metal-based coating.     -   At least one nanoparticle based on ferromagnetic metal is         configured so as to form, under the action of a magnetic field,         a coating based on ferromagnetic metal on a portion of the         surface of a substrate.     -   At least one first modified nucleic acid strand comprising at         least one first metal-based nanoparticle and/or a first metal         atom and at least one second modified nucleic acid strand         comprising at least one second metal-based nanoparticle and/or a         second metal atom, are configured so that the first and/or         second nanoparticle and the first and/or second metallic atom         form a coating based on a metal alloy or a composite on a         portion of the surface of a substrate. Advantageously, a         compound in the invention is, for example, a mixture of metal         and metal oxide, carbide and/or nitride.     -   At least one first modified nucleic acid strand comprising at         least one first nanoparticle based on a first metal and at least         one second modified nucleic acid strand comprising at least one         second nanoparticle based on a second metal are configured so         that the first and second nanoparticles form a dual-layer         coating composed of a deposition based on the first metal of the         first nanoparticle covered by a deposition of the second metal         of the second nanoparticle on a portion of the surface of a         substrate.

An advantageous non-limitative aspect is to allow depositions in cavities, optionally with high aspect ratios (for example 50) using:

-   -   A deposition solution, that is to say a deposition by liquid         method;     -   A template produced from a nucleic acid strand, this template         having a nanometric size;     -   A chemical function for grafting the template onto the required         surface.

FIG. 1 illustrates a schematic view of a modified nucleic acid double strand 100 on which a nanoparticle 20 comprising a metal compound has previously been grafted, at the periphery of the double strand, on the structure of the nucleic acid strand. Metal means something that comprises at least one metal. This strand represents a nucleic acid of the DNA or RNA type or an analogue of nucleic acid. Analogue of nucleic acid means an acid composed of a skeleton (or polymer or strand) formed by an alternation of phosphates and sugars, bases 10 nitrogenated by means of sugar, at the rate of one base 10 per sugar, being connected to said skeleton. The term “metallization” of the nucleic acid strand 100 is used when a nanoparticle 20 comprising a metal compound is grafted at the periphery or end of the structure of the strand. The pitch of the strand is around 3 nanometres and, in this example, comprises ten pairs of bases 10. The envelope surrounding the nucleic acid strand 100 is notional. The nanoparticle 20 is preferably chosen from a metal, a metal oxide, a nitride or a metal carbide. By way of example, metals such as Cu, Ag, Au, Ru or Pt can be cited; oxides of the elements Si, Cu, Al, Zr, Ti, Fe and Zn; nitrides of the elements Ti, Ta, Hf, Mo and Si; carbides of the elements Si, Ti, Ta, W, Al or Fe. The nanoparticle 20 has a diameter of between 1 nanometre and 100 nanometres.

FIG. 2 illustrates a schematic view of a modified nucleic acid double strand 100 on which there has been inserted, on the structure of the strand, an atom 40, comprising a metal compound, between two bases 10. In this case the term “metallation” of the nucleic acid strand 100 is used. The atom 40 is preferably chosen from copper, nickel, aluminium, palladium, gold or silver. The modified nucleic acid strand 100 within which an atom 40 has been grafted on the structure of the strand is of smaller size compared with a modified nucleic acid strand 100 having a grafted nanoparticle 20 at the periphery. A chemical function 60, for fixing the modified nucleic acid strand 100 on a specific three-dimensional surface, has been grafted on the periphery of the structure of the strand. According to one configuration, this chemical function 60 is grafted onto the structure of a modified nucleic acid strand 100 comprising one or more nanoparticles 20 grafted at the periphery of the structure of the strand. According to another embodiment, a nucleic acid strand 100 comprises one or more atoms 40 inserted in it and/or attached at the periphery of the structure of the strand as well as a chemical function 60 for attaching the strand to a specific three-dimensional surface of the substrate 20. Preferably, a modified nucleic acid strand 100 comprises, on the structure thereof, one or more nanoparticles 20, one or more atoms 40 and at least one chemical function 60.

The chemical function 60 is a chemical group (linker and/or spacer) able firstly to be fixed to the modified nucleic acid strand 100 and secondly to have a group of peripheral atoms having either a hydrophilic property or a hydrophobic property. It may be advantageous to have several chemical functions 60 per nucleic acid strand 100 in order to facilitate the grafting onto the substrate 200 such as for example one chemical function 60 per end.

Moreover, hydrophilicity can be obtained by a chemical group associated with the structure (or skeleton) of the nucleic acid strand 100 or integrated therein (in other words the skeleton is itself hydrophilic). The nucleic acid double strand 100 is naturally hydrophilic at the periphery. Thus it is possible to use this intrinsic property for grafting onto hydrophilic surfaces without having to add a specific chemical function 60; the latter is naturally integrated in the nucleic acid strand 100.

FIGS. 3A and 3B illustrate schematic views of a modified nucleic acid single strand 100 on which there have previously been grafted, at one of the ends thereof, on the structure of the nucleic acid strand 100, a nanoparticle 20 comprising a metal compound and at the other end a chemical function 60. The nucleic acid strand 100 is provided with at least one nanoparticle 20 and/or one atom 40 as well as a chemical function 60 that will enable the modified nucleic acid strand 100 to be grafted onto the accepter surface.

FIGS. 4 to 8 illustrate an example embodiment showing the concatenation of the technological step for integrating the metal-based coating 30 on a three-dimensional surface of a substrate 200 with a view to producing a through via. This example is purely illustrative. In particular the three-dimensional surface may comprise reliefs both in a peak and in a hollow on the surface of the substrate 200.

FIG. 4 illustrates the step of forming an interconnection pattern on the substrate 200. The pattern is produced so as to form a cavity in the substrate 200. Advantageously, the cavity has a depth greater than its width. Depth means a dimension through the thickness of the substrate 200. Width means a dimension perpendicular to the thickness of the substrate 200. According to one embodiment, the pattern forms a relief on the surface of the substrate 200. The substrate 200, or at least the portion of the substrate 200 in which the pattern is formed, is preferentially chosen from a semiconductor material. The substrate 200 is preferably made from silicon. It may be glass or polymer. For a silicon substrate 200, the step of forming the interconnection pattern may be performed by deep reactive ion etching using an SiO₂ mask for example. The etching of the substrate 200 to form the interconnection pattern is preferably anisotropic. The etching of the substrate 200 may be dry or wet.

FIG. 5 illustrates the step of treating the three-dimensional surface of the substrate 200, or at least a portion of the surface, in order to obtain, for example, a hydrophilic/hydrophobic contrast. This step is optional since some surfaces are naturally hydrophilic or hydrophobic. This is because the surface of a silicon substrate 200 is for example naturally hydrophobic while that of silicon oxide is naturally hydrophilic.

For a substrate 200 not having a hydrophilic or hydrophobic nature, a grafting layer 250 may be deposited on the substrate 200. The grafting layer 250 may be deposited according to any type of technique, for example chosen from chemical vapour deposition, physical vapour deposition, atomic layer deposition or molecular jet deposition. According to one embodiment, the grafting layer 250 comprises a hydrophilic material such as a metal oxide, such as for example silicon dioxide (SiO₂), titanium oxide (TiO₂) or aluminium oxide (Al₂O₃). According to another embodiment, the grafting layer 250 comprises a hydrophobic material such as hexamethyldisilazane (HMDS) normally used in microelectronics as a promoter of the adhesion of photolithography resins, or a fluorinated polymer such as the one used in a passivation layer in the deep etching method of the DRIE type. Note that the compounds in the family of organosilanes may be either hydrophilic or hydrophobic. The thickness of the grafting layer 250 is preferentially between a few tens of nanometres and 1 micron. When its thickness is sufficient and the properties of the material so permit, the grafting layer 250 may also serve as an electrical insulation layer. The grafting layer 250 may be deposited over the entire three-dimensional surface of the substrate 200. Preferably, the grafting layer 250 is deposited selectively on the three-dimensional surface of the substrate 200, that is to say on only a portion of the three-dimensional surface where the modified nucleic acid strands 100 must be deposited.

FIG. 6 illustrates a step of grafting, on the three-dimensional surface of the substrate 200, at least one modified nucleic acid strand 100, comprising at least one atom 40 and/or one nanoparticle 20 and at least one chemical function 60, as described previously in FIGS. 1 and 2. It is possible, in general terms, to define the chemical function 60 according to the nature of the surface (insulator, metal, etc.) on which the modified nucleic acid strand 100 will be deposited. The chemical function 60 will be suited to the treatment of the surface of the substrate 200. According to a configuration where the substrate 200 has a hydrophobic surface, the chemical function will be chosen with a hydrophobic nature so as to interact and be fixed to the three-dimensional surface of the substrate 200. According to another embodiment where the substrate 200 has a hydrophilic surface, the chemical function 60 will be chosen with a hydrophilic nature so as to interact and be fixed to the three-dimensional surface of the substrate 200.

According to an embodiment where the three-dimensional surface of the substrate 200 comprises a plurality of portions with different natures (that is to say either hydrophilic or hydrophobic), the chemical function 60 will cooperate only with the portion or portions of the surface having the same nature as it. Thus the cooperation between a chemical function 60 and the three-dimensional surface of the substrate 200 will take place selectively on the chosen portion or portions.

The step of grafting, on the three-dimensional surface of the substrate 200, at least one modified nucleic acid strand 100, comprising at least one atom 40 and/or a nanoparticle 20 and at least one chemical function 60, is obtained by putting the surface of the substrate 200 in contact with a bath comprising at least one modified nucleic acid strand 100. The bath is advantageously an aqueous solution with a concentration of nucleic acid strands 100 of between approximately 10⁻¹² and 10⁻⁶ moles/litre. The substrate 200 is immersed in the bath at ambient temperature for the time necessary, for a period for example of between one minute and a few hours, for grafting at least one modified nucleic acid strand 100 on the pretreated portions of the three-dimensional surface of the substrate 200. According to the concentration of nucleic acid strands 100 in the solution and the number of nanoparticles 20 and/or atoms 40 inserted on the structure of the nucleic acid strands 100, a thickness of metal-based coating 300 is obtained, for example, between a minimum thickness that is around the size of the nanoparticle 20 or the length or diameter of the nucleic acid strands 200 to reach a maximum thickness of a few hundreds of nanometres.

In order to increase the surface density of nanoparticles 20 and/or atoms 40 on the three-dimensional surface of the substrate 200, use will advantageously be made of a mixture of modified nucleic acid strands 100 comprising strand structures (or skeletons) with different lengths and/or sizes of nanoparticles 20 and/or atoms 40, or first the modified nucleic acid strands 100 will be grafted with the larger nanoparticles 20. According to another embodiment, the modified nucleic acid strands 100 comprising atoms 40 will be grafted first, and then the modified nucleic acid strands 100 comprising the nanoparticles 20, or vice versa. Preferably, the bath comprises both modified nucleic acid strands 100 provided with atoms 40 and modified nucleic acid strands 100 provided with nanoparticles 20.

In a particular case, it is possible to choose a mixture of a pair comprising at least a first modified nucleic acid strand 100 comprising a strand structure or a skeleton equipped with at least one nanoparticle 20 based on a metal M1 and at least a second modified nucleic acid strand 100 comprising a skeleton, which may be of a different size from the first, equipped with at least one nanoparticle 20 based on a metal M2. It is thus possible, using this mixture, to deposit a composite material formed from nanoparticles 20 M1 and M2. A composite in the invention is for example a mixture of metal and metal oxide, carbide and/or nitride. When M1 and M2 are metals, it is thus possible to form a metal alloy. It is also possible to produce a metal alloy when the two modified nucleic acid strands 100 comprise metal atoms 40 respectively M1 and M2. When M1 and M2 are for example and respectively a metal and a metal compound of the oxide, nitride or carbide type, it is possible to form a composite metal the physical properties of which, such as for example electrical or thermal conductivity and/or coefficient of expansion, are dependent on the composition of material M1 and material M2.

In a variant, it is possible to choose M1 such that it is for example associated with an oxide M1_(X)O_(Y) and M2 as a metal, such that, in contact, the two materials react (under the action of temperature, for example) in order to form a first metal M1 and a second metal oxide M2_(Z)O_(T) (produced from the second metal M2). Thus, therefore, when first modified nucleic acid strands 100 comprising the metal M2 are first of all deposited, and then second modified nucleic acid strands 100 comprising the metal oxide M1_(X)O_(Y), it will be possible to create a dual layer composed of metal M1 on the insulator M2_(Z)O_(T). According to one example embodiment, copper will be chosen as the first metal M1 and aluminium as the second metal M2.

FIG. 7 illustrates a heating step configured to partially or completely destroy the structure of the nucleic acid strand 100 and/or the chemical function 60 in order to promote the formation of the coating 300 based on atoms 40 and/or nanoparticles 20 on the three-dimensional surface of the substrate 200. The step of partial or complete destruction of the structure of the nucleic acid strand 100 and/or of the chemical function 60 may be performed at low temperature, preferably below 200° C. In order to promote the coalescence or aggregation of the metal-based nanoparticles 20 and/or metal atoms 40, an annealing can be carried out at a temperature of between 200° C. and 450° C., or even at a higher temperature compatible with the permissible thermal budget and below approximately 800° C. In order to densify the metal-based coating 300, the step of grafting a modified nucleic acid strand 100 and the heating step may be repeated.

According to an embodiment where it is then wished to deposit a metal, a chemical (electroless) deposition is carried out after the coating 300 obtained by the grafting of modified nucleic acid strands 100. For example, gold could be deposited on gold nanoparticles 20; the metal-based coating 300 being previously formed from nanoparticles 20.

FIG. 8 illustrates the step of carrying out an electrochemical deposition (ECD) on the metal-based coating 300.

FIG. 8 illustrates a view in section according to the prior art of a through via of the TSV type filled in accordance with the current methods. In the methods based on the use of a silicon substrate 200, the succession of steps consisting of the production of a through via comprises, at the end of the step of etching the substrate 200, the step of depositing an insulator and the step of depositing a layer that is a barrier to the diffusion of metal (for example copper), a step consisting of covering and/or filling the via with an electrical conductor (for example copper), generally by electrodeposition. A chemical and mechanical polishing step may be performed at the end of this concatenation with a view to eliminating the excess metal on the surface of the substrate 200. Thus the through via will emerge on a first face of the substrate 200 from which the etching of the cavity is performed. The through via will be obtained after thinning of a second face of the substrate 200, opposite to the first face.

FIGS. 9A and 9B illustrate an example of a three-dimensional surface on which the metal-based coating 300 according to the present invention can be produced while ensuring uniformity of the layer and distribution over the entire three-dimensional surface of the substrate 200. The majority of the traditional deposition methods (of the CVD, ALD, PVD, etc. type) do not make it possible to produce a uniform deposit on patterns. It proves to be actually difficult to form a uniform coating on a three-dimensional surface having hollow patterns and/or in relief. In a particularly advantageous manner, the method according to the invention will make it possible to produce a uniform metal-based coating 300 perfectly following the topography of the three-dimensional surface of the substrate 200.

In FIG. 9A, the modified nucleic acid strands 100, comprising at least one nanoparticle 20 and/or one atom 40 and at least one chemical function 60, are fixed on the pretreated hydrophilic or hydrophobic portions of the surface of the substrate 200 or on the grafting layer 250 of the three-dimensional surface of the substrate 200.

FIG. 9B illustrates the coating 300 obtained after grafting of the modified nucleic acid strands 100 on the pretreated portions of the three-dimensional surface of the substrate 200. Advantageously, the metal-based coating 300 covers all the flanks and angles of the three-dimensional surface of the substrate 200 with the same thickness and the same uniformity.

FIG. 10A illustrates an example of a three-dimensional surface of a substrate 200 on which a cavity was previously produced. The flanks of the cavity are covered with a hydrophilic or hydrophobic film, that is to say with the grafting layer 250, for fixing the modified nucleic acid strands 100 comprising at least one nanoparticle 20 and/or at least one atom 40 and at least one chemical function 60. Advantageously, at the end of the method according to the invention, the metal-based coating 300 is deposited on all the flanks of the cavity formed in the substrate 200.

FIG. 10B illustrates an example of a three-dimensional surface of a substrate 200 on which a cavity has previously been produced. In order to make a localised deposition on a selective portion of the substrate 200, a mask may advantageously be produced by the overhanging over the cavity formed in the substrate 200. Following an irradiation by ultraviolet rays, only the flanks of the cavity protected from the rays are covered with modified nucleic acid strands 100. When a surface is exposed to an ultraviolet radiation, it has a tendency to become hydrophilic. Thus, according to an embodiment in which the three-dimensional surface of the substrate 200 is naturally or pretreated so as to be hydrophobic, the chemical functions 60 chosen with a hydrophobic nature will come to be fixed on the hydrophobic portions of the three-dimensional surface. The portions exposed to ultraviolet radiation, which have become hydrophilic, will no longer be able to cooperate with the chemical function 60 and, consequently, the modified nucleic acid strands 100 will not be able to be deposited on the exposed portions. Advantageously, this embodiment makes it possible to effect a selective grafting under irradiation by ultraviolet rays. According to another embodiment where the three-dimensional surface of the substrate 200 is naturally or pretreated so as to be hydrophobic and the chemical functions 60 chosen with a hydrophilic nature, some hydrophobic portions of the surface of the substrate 200, after irradiation by ultraviolet radiation, will become hydrophilic and will therefore be able to interact with the also hydrophilic chemical functions 60.

The present invention makes it possible to produce a metallic or insulating coating 300 on a three-dimensional surface comprising monolayers of nanoparticles 200 based on metal and/or metal atoms 40. One of the advantages of the present invention consists of the use of a wet method for effecting the deposition, promoting a uniform and continuous deposition on a three-dimensional surface of the substrate 200.

It therefore appears that it is possible to deposit nanoparticles 20 based on metal (gold, nickel, for example) or insulating nanoparticles (SiO₂, TiO₂, for example) on a hydrophilic surface or a hydrophobic surface. The technique appears to be very versatile and could therefore make it possible to graft any type of nanoparticle 20 on any type of surface with, in some cases, the possibility of localising the deposit under ultraviolet irradiation through a photolithography mask.

The size of the nucleic acid strands 100, of around one nanometre, makes it possible, in a particularly advantageous fashion, to penetrate cavities with a high aspect ratio. Because of the size of the strand, it therefore appears possible to have a nanometric template for positioning nanoparticles 20 or atoms 40 on surfaces with relief and in particular through vias with a high aspect ratio, approaching 50:1.

Particularly advantageously, it is possible, under the action of a magnetic field, to selectively and in a directed fashion deposit modified nucleic acid strands 100 comprising at least one ferromagnetic nanoparticle 20. A ferromagnetic material, when it is immersed in a magnetic field, generates a new magnetic field within it. This phenomenon is more commonly called magnetisation.

The method according to the present invention opens the door to high-density three-dimensional integration. This invention makes it possible to collectively effect 3D (or even 2D also) deposits on substrates 200 of the silicon or silicon-oxide type or based on silica. It makes it possible in particular to produce high-density TSV through vias in substrates where it is necessary to electrically connect the substrates to each other. It applies to the manufacture of microelectronic systems. According to the invention, microelectronics means all microelectronic and nanoelectronic techniques. In addition to the applications for the deposition of coatings or layers described above, the multilayer structures according to the invention advantageously can be used in the form of capacitances as energy accumulators or filtering elements in many electronic products such as integrated electrical supplies, signal amplifiers and radio-frequency (RF) circuit filters and for all kinds of domestic applications, or for the motor industry and the telecommunications industry where miniaturisation brings advantages of reliability and cost reduction. The devices that can be formed can fit in microelectromechanical (MEMS) and/or optical systems.

The present invention is not limited to the embodiments described above but extends to any embodiment covered by the claims. The invention does not apply solely to a three-dimensional surface but also to a two-dimensional surface. 

1. A method for producing a metal-based coating on at least one portion of the surface of a substrate of a microelectronic device, wherein it comprises: using a modified nucleic acid strand comprising a nucleic acid strand structure, at least one metal-based nanoparticle and/or a metal atom and at least one chemical function, at least one step of fixing the modified nucleic acid strand to the portion of the surface of the substrate; said portion of the surface of the substrate being a three-dimensional surface in the form of a cavity.
 2. The method according to claim 1, wherein the step of fixing the modified nucleic acid strand is performed by means of the chemical function.
 3. The method according to claim 1, wherein the method comprises a step of at least partial destruction of the nucleic acid strand structure and/or of the chemical function.
 4. The method according to claim 3, wherein the step of at least partial destruction of the nucleic acid strand structure and/or of the chemical function comprises a heating step configured so as to partially or completely destroy the structure of the nucleic acid strand and/or of the chemical function.
 5. The method according to claim 1, wherein the cavity has a depth greater than its width.
 6. The method according to claim 1, wherein the step of fixing the at least one modified nucleic acid strand on the portion of the surface of the substrate is obtained by putting the surface of the substrate in contact with a bath comprising at least one modified nucleic acid strand.
 7. The method according to claim 1, wherein the portion of the surface of the substrate comprises a chemical group configured so as to interact with the chemical function fixed on the structure of the at least one nucleic acid strand.
 8. The method according to claim 1, comprising several steps of fixing modified nucleic acid strands.
 9. The method according to claim 8, wherein the modified nucleic acid strands are identical or different through the structure of their respective strands and/or through their respective chemical functions and/or through the nature and/or dimensions of the metal-based nanoparticles and/or the metal atoms.
 10. The method according to claim 8, comprising, after the steps of fixing modified nucleic acid strands, a single step of destruction of the nucleic acid strand structures.
 11. The method according to claim 1, comprising, prior to said at least one step of fixing the at least one modified nucleic acid strand on the portion of the surface of the substrate, a step of deposition of a grafting layer on at least the portion of the surface of the substrate.
 12. The method according to claim 1, wherein the portion of the surface of the substrate or the grafting layer comprises a hydrophilic or hydrophobic material.
 13. The method according to claim 1, wherein the chemical function is a group of hydrophilic or hydrophobic atoms.
 14. The method according to claim 1, wherein the metal-based coating forms part of a via.
 15. The method according to claim 1, wherein the metal atom is chosen from copper, nickel, aluminium, palladium, gold or silver.
 16. The method according to claim 1, wherein the metal-based nanoparticle is chosen from a metal, a metal oxide, a metal nitride or a metal carbide.
 17. The method according to claim 1, comprising, prior to the step of fixing the at least one modified nucleic acid strand on the portion of the surface of the substrate, a step of irradiating, by ultraviolet radiation, the portion of the surface of the substrate intended to receive the metal-based coating.
 18. The method according to claim 1, comprising, prior to the step of fixing the at least one modified nucleic acid strand on the portion of the surface of the substrate, a step of irradiating, by ultraviolet rays, the entire surface of the substrate except for the portion of the surface intended to receive the metal-based coating.
 19. A The method according to claim 1, comprising the use of at least one nanoparticle with a diameter of between 1 nanometre and 100 nanometres.
 20. Use of at least one modified nucleic acid strand comprising a nucleic acid strand structure, at least one metal-based nanoparticle and/or a metal atom said structure being configured so as to form a metal-based coating on a three-dimensional portion of the surface of a substrate, said portion being a cavity.
 21. Use according to claim 21, wherein the modified nucleic acid strand comprises at least one metal-based nanoparticle, said metal being a ferromagnetic metal, said nanoparticle being configured so as to form, under the action of a magnetic field, a coating based on ferromagnetic metal on a portion of the surface of a substrate.
 22. Use according to claim 21, wherein: at least one first modified nucleic acid strand comprising at least one first metal-based nanoparticle and/or one first metal atom, and at least one second modified nucleic acid strand comprising at least one second metal-based nanoparticle and/or one second metal atom, are configured so that the first and/or second nanoparticle and the first and/or second metal atom form a coating based on a metal alloy or a composite on a portion of the surface of a substrate.
 23. Use according to claim 21, wherein: at least one first modified nucleic acid strand comprising at least one first nanoparticle based on a first metal, and at least one second modified nucleic acid strand comprising at least one second nanoparticle based on one second metal, are configured so that the first and second nanoparticles form a dual-layer coating composed of a deposit based on a first metal of the first nanoparticle covered by a deposit of the second metal of the second nanoparticle on a portion of the surface of a substrate.
 24. Use according to claim 21, comprising the use of a nanoparticle having a diameter of between 1 nanometre and 100 nanometres.
 25. The method according to claim 9, wherein the modified nucleic acid strands are different through the structure of their respective strands and/or through their respective chemical functions and/or through the nature and/or dimensions of the metal-based nanoparticles and/or the metal atoms. 